1. Field of the Invention
The present invention relates to a device for producing an overtone-rich, sporty exhaust sound in four-cylinder engines.
2. Description of the Related Art
It is known in the art that motor vehicles equipped with six-cylinder, eight-cylinder or twelve-cylinder engines produce an exhaust sound which is considered particularly sporty by the customer. It is also known that motor vehicles equipped with four-cylinder engines do not produce such a sporty exhaust sound. Since it is not possible for reasons of cost and other reasons that each motor vehicle is equipped with a six-cylinder, eight-cylinder or twelve-cylinder engine, many attempts have been made to change the exhaust system of motor vehicles with four-cylinder engines in such a way that they produce a sportier sound. However, most of these measures only increase the amplitude of the sound at the outlet opening of the exhaust system at small rates of rotation and particularly during idle operation by acoustically switching off portions of the exhaust muffler. The exhaust sound becomes louder as a result of these measures, however, the known and popular exhaust sound of six-cylinder, eight-cylinder and twelve-cylinder engines is still not achieved.
When the exhaust sound of four-cylinder engines is analyzed, it is found that it contains the second, fourth, sixth, eighth, etc., harmonic of the basic frequency determined by the rate of rotation of the engine. When analyzing the exhaust sound of six-cylinder, eight-cylinder and twelve-cylinder engines in a similar manner, it can be found that it also contains the first, third, fifth, seventh, etc. harmonic and, depending on the type of engine, also the 1.5th, 2.5th, 3.5th, etc., harmonic of the basic frequency. These harmonics produced by the higher number of cylinders are completely lacking in the four-cylinder engine.
Therefore, it is the primary object of the present invention to provide a device which makes it possible also in four-cylinder engines to produce an overtone-rich, so-called sporty exhaust sound without increasing the amplitude of the exhaust sound.
In accordance with the present invention, in an exhaust system of a four-cylinder engine essentially composed of exhaust gas-conducting pipes with at least four manifold pipes, at least one front pipe and a tail pipe, the above object is met by selecting the length and/or cross-section of at least one of the exhaust pipes different from the length and/or cross-section of the other exhaust pipes, wherein at least some of the exhaust pipes lead into a first, second and/or third collecting point.
The present invention is based on the principle of delaying the sound events produced in the four cylinders of the engine at different times by providing different lengths and cross-sections of the exhaust gas-conducting pipes, so that superpositions occur at the collecting points of the pipes which correspond to a pulse pattern as it is known from six-cylinder, eight-cylinder or twelve-cylinder engines and, therefore, also contain the first, third, fifth, seventh, etc. harmonic and possibly the 1.5th, 2.5th, 3.5th, etc., harmonic of the basic frequency. It has been found in this connection that the exhaust sound subjectively even becomes quieter because the sound energy previously only contained in the second, fourth, sixth, etc., harmonic is transferred into the newly produced harmonics. In addition, the transformation is achieved equally well in the entire frequency range, as compared to previous solutions in which it was attempted to couple the lacking harmonics into the exhaust system by means of loudspeakers.
In accordance with a first embodiment of the invention, the length and/or cross-section of at least one manifold pipe deviate from the length and/or cross-section of the other manifold pipes. This makes it possible to produce the 1.5th, 2.5th, 3.5th, etc., harmonics.
In accordance with another embodiment of the invention, two front pipes are provided wherein the length and/or cross-section of one front pipe differ from the length and/or cross-section of the other front pipe. This makes it possible to produce the third, fifth, seventh, etc., harmonics of the basic frequency.
In accordance with a modification of the invention, at least two manifold pipes lead into the first collecting point where a front pipe begins. The two other manifold pipes can be combined at a second collecting point, as is the case in conventional four-cylinder engines.
However, it is also possible to combine three manifold pipes in a collecting point, wherein the front pipe following this collecting point is combined downstream with the fourth manifold pipe in a second collecting point.
In accordance with another embodiment of the invention, two collecting pipes are provided which lead into the third collecting pipe, wherein the length and/or cross-section of one of the collecting pipes deviate from the length and/or cross-section of the other collecting pipe.
Other possible measures for producing overtones are to couple a resonator space to at least one manifold pipe and/or collecting pipe, or to mount a screen, a nozzle, a valve and/or a catalyst body into at least one manifold pipe and/or collecting pipe.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.